This application corresponds to P-2000-209143 and P-2000-248110 filed in Japan on Jul. 11, 2000 and Aug. 18, 2000; the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a positioning system that uses absolute sensors to detect the position of a control object and, based on the detection result, moves the control object to a target position.
2. Description of the Prior Art
Absolute sensors such as optical absolute sensors and resolvers, differential transformers, potentiometers and the like are used for detecting the absolute position of objects that undergoing rotational or linear movement. Positioning systems that use such absolute sensors to control the positioning of a control object are usually equipped with a plurality of absolute sensors for multi-axial positioning control. In these systems, the multi-axial drive mechanisms are controlled to move the object to the target position based on detection signals from the absolute sensors.
The positioning system is equipped with a control system apparatus constituted by a microcomputer. Detection signals from the absolute sensors are input to the control system apparatus via an A/D conversion board and digital I/O board and the like. When the absolute sensors that are connected to a system are sensors such as resolvers and differential transformers that need to be driven by, for example, an excitation signal, such excitation is effected by means of a special-purpose transformer.
The number of absolute sensors that can be connected to a positioning system is limited by the number of signal bits. Usually only one sensor can be connected to an A/D conversion board. In the case of a digital I/O board, the number of sensors, which is to say the sensor resolution, depends on the number of bits. Thus, in order to connect the required number of sensors, the system configuration has to be modified by increasing the number of A/D conversion boards and digital I/O boards, which is complicated.
Moreover, when a plurality of sensors are connected to the system, a problem has been that, because the driving of the sensors cannot be individually controlled, each sensor has to be maintained in drive mode, which is not efficient.
An object of the present invention is to provide a positioning system having a plurality of absolute sensors that can readily be configured.
Another object of the present invention is to provide a positioning system having a plurality of absolute sensors the drives of which can be switchably controlled.
To attain the above and other objects, the invention provides a positioning system comprising a drive mechanism that moves a control object to a target position, absolute sensors that detect an absolute position of a control object moved by the drive mechanism, a control apparatus that controls the drive mechanism based upon detection results of the absolute sensors, and an interface apparatus via which absolute sensor output signals are input into the control apparatus;
the control apparatus being comprised by a personal computer and the interface apparatus being comprised by a PC card inserted into a card slot in the PC.
The PC card can include sensor connection terminals to connect the absolute sensors, a converter that converts signals input via the sensor connection terminals to digital position signals, PC connection terminals for supplying signals output from the converter to the PC, and a sensor drive circuit that supplies the absolute sensors with electrical drive power.
The PC card can also include a plurality of sensor connection terminals and a sensor switching circuit for switching between the sensor connection terminals and the converter in accordance with commands from the PC. In the case of such a configuration, preferably the sensor switching circuit should also switch the sensor connection terminal that is supplied with electrical drive power from the sensor drive circuit.
It is also preferable for the sensor drive circuit to include at least one selected from: resolver excitation circuit, differential transformer excitation circuit, potentiometer drive circuit, and optical or magnetic absolute encoder drive circuit.
It is preferable for the converter to include at least one selected from: a conversion unit for converting resolver output signals to digital position signals, conversion unit for converting differential transformer output signals to digital position signals, and a conversion unit for converting potentiometer output signals to digital position signals.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and following detailed description of the invention.